1. Field of the Art
The present invention generally relates to an electric-component ("EC") feeder which feeds a carrier tape carrying electric components ("ECs") (e.g., electronic components) at a predetermined component-carry pitch, and thereby supplies the ECs, and particularly to the improvements of the feeding of the carrier tape.
2. Related Art Statement
There is known an EC feeder which feeds a carrier tape carrying ECs at a predetermined component-carry pitch, at a tape-feed pitch equal to a quotient obtained by dividing the component-carry pitch by an integral number, and thereby supplies the ECs, one by one, to an EC-taking position. A carrier tape may be fed in various manners. For example, Japanese Patent Application laid open for public inspection under Publication No. 7(1995)-9381 discloses an EC feeder wherein a drive source for feeding a carrier tape is not provided on a main frame of the feeder. This feeder is employed in an EC mounting system so as to supply ECs to an EC mounting device of the EC mounting system. The EC mounting device includes an intermittent-rotation body which is intermittently rotatable about a vertical axis line at a predetermined rotation-angle pitch; and a plurality of EC-suction heads as a plurality of EC-holding heads that are provided on the intermittent-rotation body such that the EC-suction heads are equiangularly spaced from each other about the axis line at a predetermined spacing-angle pitch equal to the rotation-angle pitch. As the intermittent-rotation body is intermittently rotated by a drive device which includes a servomotor as the drive source, the EC-suction heads are sequentially moved to an EC-sucking position, an EC-mounting position, etc. The drive device further includes a drive member which is provided at a position corresponding to the EC-sucking position; a driven member which is provided on the main frame of the EC feeder; and a motion converting device which includes a cam and a cam follower and which transmits the drive force of the above-indicated servomotor to the drive member so as to drive the driven member and thereby feed the EC carrier tape at a predetermined tape-feed pitch.
On the other hand, Japanese Patent Application laid open for public inspection under Publication No. 8(1996)-23190 discloses an EC feeder wherein a drive source is provided on a main frame of the feeder. This feeder employs an air cylinder as the drive source, and feeds a carrier tape by utilizing the advancing and retracting movements of a piston rod of the air cylinder. Since the drive source is provided on the main frame, the carrier tape can be fed at a free timing.
Japanese Patent Application laid open for public inspection under Publication No. 10(1998)-112598 discloses an EC feeder wherein a stepper motor as a sort of electric rotary motor is provided on a main frame of the feeder, as a drive source for feeding a carrier tape.
In any manner, it is preferable to start and stop the feeding of the carrier tape with the least possible vibration. For example, in the case where the carrier tape includes an accommodating tape having, at the predetermined component-carry pitch, a plurality of accommodating pockets which accommodate the plurality of ECs, respectively; and a cover tape which is attached to the accommodating tape to close the accommodating pockets, each of the ECs is moved to the EC-taking position, by the feeding of the carrier tape, after the cover tape has been peeled from the accommodating tape. If the vibration produced when the feeding of the carrier tape is started or stopped is great, each EC may jump out of the accommodating pocket, or may change its posture in the pocket. In the latter case, each EC-suction head may fail to hold the EC.
In the case where there are no limitations to the time that can be used to feed the carrier tape, the tape may be fed at low speed, acceleration, and deceleration, so that the feeding of the tape may be started and stopped with little vibration. However, in many cases, there are some limitations. For example, in the EC mounting system, disclosed in the above-indicated Japanese patent document 7-9381, in which the EC feeder is employed for supplying the ECs to the EC mounting device, the efficiency with which the ECs are mounted on a circuit substrate such as a printed-circuit board is improved by shortening the head-operation cycle time defined as the time that is needed to rotate each EC-suction head to a stop position (i.e., an operation station) after the prior EC-suction head is rotated to the stop position. Shortening the head-operation cycle time needs feeding quickly each EC to the EC-taking position.
In the EC feeder disclosed in the above document, the motion converting device which includes the cam and the cam follower transmits, to the drive member, the rotation of the servomotor as the drive device for the intermittent-rotation body. However, the shape of the cam is not determined such that the drive member drives the driven member such that the feeding of the carrier tape is started and stopped with little vibration. Consequently the carrier tape is vibrated. To solve this problem, the leading portion of the carrier tape is covered by a cover member, and the cover member is moved with the tape when the tape is fed. Thus, each EC is prevented from jumping out of the accommodating pocket. When each EC-suction head takes the EC from the pocket, the cover member is moved away from a position right above the EC, to allow the head to take the EC. However, this arrangement is not simple.
In the case where the air cylinder as the drive source is provided on the main frame of the EC feeder, a motion converting device which includes a ratchet wheel, a sprocket, and a pivotable member with a ratchet pawl converts the advancing and retracting movements of the piston rod of the air cylinder, into the feeding of the carrier tape. In this case, too, the feeding of the carrier tape is started and stopped with vibration.
Moreover, in the case where the stepper motor as the drive source is provided on the main frame of the EC feeder, the feeding of the carrier tape is started and stopped with little vibration, and the tape is fed at a high speed, since the stepper motor can be controlled with respect to its rotation speed and its stop position. However, the stepper motor itself is expensive, and it is difficult to employ a control device which controls the stepper motor with accuracy. Thus, this feeder costs high.